Process for upgrading isomerizable hydrocarbon compounds



Sept. 6, N. L. CARR PROCESS FOR UPGRAOING ISOMERIZABLE HYDROOARBON COMPOUNDS Filed Dec. 19. 195s ATTORNEY performance characteristics.

PROCESS FOR UPGRADING ISOMERIZABLE HYDROCARBON COMPOUNDS Norman L. Carr, Crystal Lake, lll., assignor to The Pure Oil Company, Chicago, Ill., a corporation of Ohio Filed Dec. 19, 1956, Ser. No. 629,318

9 Claims. (Cl. 208-66) This invention relates to the production of high octane number motor fuels. It is more directly concerned with upgrading isomerizable hydrocarbon constituents boiling in the gasoline motor fuel range.

In la refining situation wherein such factors as highcost crude petroleum oils and upward trends in the quality of gasoline type motor fuels are present, there are economic advantages in processing the normally gaseous hydrocarbons to produce liquid products and in upgrading the several liquid gasoline components which have low Some light, gaseous ends can be converted to high octane number blending constituents by such processes as alkylation and polymerization. The octane ratings of the n-C-C7 hydrocarbons in the gasoline range are best increased by isomerization. To

` effect this isomerization, there has been developed a number of processes which employ several types of catalysts.

Earlier-developed processes, such as the Shell liquid phase isomerization process and the 'Isomate process of Standard Oil Co.` (Ind), employed AlCla-containing catalysts. It is preferable, however, to use non-corrosive,

solid catalysts which can be more easily handled in this i Vemploying platinum or palladium supported on a suitable catalytic support as the isomerization catalyst. To obtain maximum upgrading in the engine performance characteristics of low boiling petroleum distillates, consideration must therefore be given to the eicient processing of the normal, saturated paratiinic components which contain seven carbon atoms.V

It is therefore `a primary object of this invention to provide an integrated process for' enhancing the octane number of n-heptane-containing, light petroleum distillates utilizing two reaction systems, each containing specie catalysts and operated under different conditions to effect quality enhancement.

this invention.

i* United States Patent O Vtively upgrading n-pentane and n-hexane.

ICC

herewith) by preconditioning the catalyst in a certain prescribed manner, described in the aforementioned applications, prior to use. This technique, in essence, comprises incorporating a minor amount of a hydrogenation component in a refractory, mixed oxides base composited to'evince acidic` properties 4and hydrocarbon cracking activity substantially in accordance with conventional catalyst preparation techniques. The freshly prepared, green catalyst is activated in a reducing atmosphere in accordance with the prior art to effect reduction of the hydrogenation component of the catalyst as far as possible under specific conditions. Thereafter, the catalyst is subjected to the `additional activation and conditioning treatment described in the above-mentioned applications. In carrying out this preconditioning phase of the catalyst preparation, the composite catalyst is subjected to an oxidizing atmosphere maintained :at a temperature of about 650 F. to 750 F. Following this oxidation, the

oxidized catalyst is contacted with hydrogen at the same temperature as that at which the oxidation was carried out to reduce the reducible elements of the composition and produce a composite catalyst of high .activityand resistance to degeneration.

It has been found that this composite catalyst effectively and ethciently upgrades n-heptane, a gasoline component having a zero octane rating, in addition to effec- Generally, n-heptane is present in isomerizable petroleum feed stocks in concentrations of about l0 to 15% by volume. When isomerizing a C5C7 petroleum fraction in the presence of the above-described preconditioned catalyst composite, it has been found that pentane, hexane, and heptane each require different operating conditions for optimum conversion. It has also been found that these optimum conditions differ from those employed in processes utilizing platinum or palladium on silica-alumina or other similar acidic supports, especially with regard to temperatures, liquid volume hourly space velocities, and hydrogen/hydrocarbon mole ratios. Optimum pentane isomerization requires more severe conditions, i.e., higher temperatures, than do hexane or heptane, and, when isomerizing a C5C7 fraction at high levels of pentane conversion, the

`requisite high temperatures decompose part of the heptanes, resulting in significant yield reduction through hydrocracking To avoid this inimical result, it is necessary to compromise by balancing conversion against yield loss with an attendant loss in operating etiiciency. According to this invention, this compromise can be avoided, 'and maximum operating eiciency maintained, by a split treatment of the C5-C7-containing feed stock, utilizing separate reaction systems. In this process, `an isomerizable feed stock, containing C5-C7 hydrocarbons, is fractionated into a light fraction consisting essentially of pentanes and a heavier fraction containing normal C6 and C7 hydrocarbons. The light and heavy fractions are then isomerized separately under optimum isomerization conditions, employing different operating conditions,

This and other objects willi" be apparent from the following detailed description of The ligure is a schematic ow diagram illustrating the ess, Serial Number 619,376, and led October 31, 1956,

and different catalysts, in each reactor. A consolidated fractionatlon system performs the necessary feed preparation, product recovery, and recycle splitting. The

Vbasic concept of this invention may be broadened to cover a split treatment wherein a C5-C6 fraction is treated separately from a C7 fraction or wherein the C5, CB and C7 low. The overhead from tower 11, comprising isopenfractions `are all isomerized separately.

Referring to the ow diagram shown in Figure 1, feed stock, such as a stabilized natural gasoline or low-boiling petroleum naphtha containing C5-C7 hydrocarbons, is introduced into the consolidated fractionating `system through line 10 and is depentanized in tower 11 after joining depropanized reaction effluent as discussed betane and normal pentane, passes through line 12 to deisopentanizer 13 wherein a fraction rich in isopentane lis separated and sent to storage through line 14. -A rst feedstock, consisting essentially of normal pentane, is ,recovered as bottoms from depentanizer 13 and passed to heater 15 through line 16. Hydrogen-rich gas is introduced into line 16 through line 17 from a source which will hereinafter be discussed, forming a first reactor charge. This rst reactor charge is heated to an elevated Vtemperature and introduced into pentane reactor 18 Vthrough line 19 to provide a iirst reaction etiluent which ,is processed as hereinafter described.

The bottoms from `depentanizer tower 11 are transferred directly to deisohexanizer 20. The isohexane fraction is separated and passed overhead through line 14. The bottoms fraction from deisohexanizer 20 is trans- ;ferred through line 21 to dehexanizer 22 from which overhead, comprising essentially pure hexane, is transferred through line 23 to a point of confluence with line 24 through which is being transferred the bottoms frac- ,.tion, comprising normal heptane, from heptane tower 25. Bottoms from deheXanizer 22 are transferred to heptane tower 25 through line 26. Overhead from dehex- Yanizer 22 and bottoms from heptane tower 25, after combining, are joined by hydrogen-rich recycle gas from line 27 to form a second reactor charge which passes through line 28, heater coil 29 and line 30 to one of al- A ternative reactors 31 and 32.

Reaction eiliuent from pentane reactor 18, flowing through line 33, joins reaction el'liuent from hexane-heptane reactor 31 or 32, flowing through line 34 to form stream 35 which flows to separator 36. In separator 36, hydrogen-rich recycle gas is separated from the combined reactor eflluents and is transferred through line 37 to branch lines 17 and 27 for combination with first and second reactor feeds owing through lines 16 and 15, respectively.

Separated liquid from separator 36 flows through line 38 to depropanizer 39 wherein a propane and lighter fraction is separated for removal from the system through line 40. Depentanizer reaction eliiuent is withdrawn from depropanizer 39 through line 41 for combination 4 NiMoO., incorporated in a /50 silica-alumina carrier prepared in accordance with the copending application of Norman L. Carr, Serial Number 619,404, tiled October 3l, 1956, now U. S. Patent No. 2,917,566, granted December 15, 1959, entitled, Catalyst and Process, and with a noble metal catalyst comprising 0.5 wt. percent platinum deposited on an alumina support were compared. This latter catalyst is a commercially available composition, and is prepared in accordance with prior art techniques. In Table I is summarized optimum yield per pass for individual hydrocarbon components obtainable when using the above base metal catalyst. For determining ultimate yield, it is assumed that perfect isomer fractionation and recovery are obtained with only the normal component being recycled for reprocessing.

TABLE I Typical optimum yield per pass for individual components [Isomerization over N iMo O4-Si0 r-AlgOg catalyst] EXEMPLARY OPERATING CONDITIONS Using the foregoing preconditioned NiMoOr-silicaalumina composite, a mixture of isomerizable hydrocarbons comprising 33.3 vol. percent n-pentane, 33.3 vol. percent n-hexane, and 33.3 vol. percent n-heptane was isomer-ized at a pressure of 350 p.s.i., a hydrogen/hydrocarbon mol ratio of 3, and a liquid volume hourly .space velocity of 1 at several reaction temperatures. The results of these runs are tabulated in Table IL Similar results are obtained with other mixtures of C5, C6, and C7 hydrocarbons.

TABLE 11 Operation on mixed feed 1 (pentane, hexane and heptane) [NlMOOf-SlOr-AlgOg Catalyst] Temperature 660 F. 710 F.

Isomer Con- Recyele- Isomer Con- Recycle- Yield Selecversion, To Yield Selecversion, To Component In Feed per Pass, tivity, Mol Fresh per Pass, tivlty, Mol Fresh Mol Percent Percent Feed Mol Percent Percent Feed Percent Ratio Percent Ratio Average 43 90. 2 2. 43 55. 5 80. 5 0. 57

l Based on perfect isomer-normal separation and recycle of normal component only, selectivity is equivalent t0 ultimate isomer yield.

Recycle to fresh feed ratio= seieenvnpmnmte yield: R=recycle rate, pure reactant.

F=feed rate, pure reaetant.

z=fracti0nal conversion/pass.

xl=fractional yield/pass.

with fresh feed entering through line 10 and ultimate separation of high octane isomeric constituents, which are removed through line 14 as product, and normal paratrinic constituents which are recycled to the pentane and hexane-heptane reactors.

Inthis investigation, results obtainable with a precon- H ditioned isomerization catalyst comprising 10 wt. percent 75 (Hna :c F

which is favorableto the isomerization of n-pentane and n-hexane it is noted that even though the isomer yield perpass is increased because of higher conversion, the ultimate yieldof isomer has been deleteriously affected. The disadvantages of carrying out the isomerization using mixed feed stocks containing n-heptane is further illustrated in Table III wherein is shown that increased conversion and resulting yield are obtained' in the processuing of only n-pentane or n-hexane, per se, at these latter operating conditions.

TABLE III Operation on normal pentane or normal hexane Isomer Selec- Con- Recycle- Yield, tivity, version, to Component Mol Percent Mol Fresh Percent Percent Feed Ratio n-Csu. 40 85 7. 1 l. 12 n-O 68 l90 75.6 0.32

To illustrate the advantages of the instant invention, a feed stock was prepared to provide a low-boiling frac- .tion` consisting essentially of n-pentane and a high-boiling l fraction consisting essentially of n-hexane and n-heptane.

`In processing the high-boiling fraction at a temperature of 660 F., employing the exemplary operating conl ditions shown in Table I, the results summarized in Table -IV are obtained.

TABLE IV Operation on normal hexane-normal heptane mixture at 660 F.

Isomer Selec- Con- Recycle- Yield, tivity, version, to

Component Mol Percent Mol Fresh Percent Percent Feed Ratio n-o .f-

52 97 53. o. 87 n-C1 66 87. 5 75. 4 0. 33

Average- 59 92.3 G4. 0.60

The low-boiling, pentane-containing fraction was processed with the hereinbefore-described, platinum-containing catalyst. The results of processing this fraction are summarized in Table V.

TABLE V Hydrosomerization of n-pentane over a platinum reforming catalyst In contradistinction to the excellent results obtainedin i the isomerization of n-pentane, noble metal catalysts are not eicient for upgrading n-heptane fractions. Upon combining the liquid products obtained in these respective processes, a C5-lblending stock is obtained having Research Octane Numbers of 74.8, without tetraethyllead,

, and*93.5 with 3 cc. of TEL/gal., on a naphthene-free basis. With a typical naphtha feed containing naphthenes,

'these numbers are several units higher.

. It is therefore apparent that the split-stream treatmentI of an isomerizable mixture containing C5-C7 hydrocarbons, comprising processing the n-pentane constituent at elevated temperatures and pressures favorable to the y isomerization of pentane in the presence of a supported ,Hq/Hydrocarbon mole ratio platinum or palladium catalyst, and processing the higherboiling constituents of the mixture at less. severe isomerization' reaction 4conditions in the presence of a pre-conditioned, acidic mixed oxides base-hydrogenation agent, composite isomerization catalyst, is superior to treatment of the entire CTC-,fraction over either of these catalysts. Furthermore, the split treatment can be carried out with infrequent regeneration with sulfur-containing or sulfurfree feedstocks and low ratios of hydrogen. These features, in combination with the highly eflcient hexaneheptane processing using the preconditioned base-metal catalyst, provide an operational scheme which is far superior to processing schemes using a full-boiling-range stock containing n-C-n-Cq hydrocarbons: as an isomerization feed. It is therefore evident that the split treatment of C5-C7-hydrocarbon-containing feed stocks in accor-dance with this invention has economic advantages in providing high pentane conversions and high overall yields of high octane products which can be used advantageously as blending stocks in gasoline formulations.

In the process of this invention the pentane isomerization catalyst comprises platinum or palladium supported on a cracking catalyst. Catalysts of the noble metal type, which are well known in the prior art and which are used in the pentane isomerization phase of this invention, contain about 0.01 to 1.0% by weight of platinum, or 0.5-2.0 weight percent of palladium on a cracking catalyst such as silica-alumina, silica-zirconia, 'silica-alumina-zirconia etc., or on activated alumina. such catalysts are contained in a number of U.S. patents such as 2,478,916', 2,479,109; 2,479,110; 2,589,189; 2,750,329; and others. Operating conditions for carrying out the pentane isomerization in the presence of a platinumor palladium-containing catalyst are selected to attain optimum results. Accordingly, the following con dtions are employed:

l Range Preferred Temperature, F S30-9004 S50-875 Pressure, p.s.i. 20G-500 S50-500 Liquid Weight Hourly Space Veloc 2-10 2-4 The isomerization of the higher-boiling fraction of the feed stock, containing n-C6 and n-Cr, hydrocarbons, is carried out in the presence of a preconditioned catalyst composite of improved efficiency prepared in accordance with 'catalyst comprising a minor amount of hydrogenatilon component incorporated in a refractory, mixed oxides base formulated to evince acidic properties and hydrocarbon cracking activity substantially in accordance with conventional catalystpreparation techniques. This catalyst is activated in accordance with the prior art toelfect reduction of the hydrogenation component of the catalyst to its most reduced state` under the conditions employed in the preparation. Subsequently, the composite catalyst is preconditioned by exposing -it to an oxidizing atmosphere maintained at a temperature of about 650 F. to 750 F. Following this oxidation the oxidized catalyst is contacted with hydrogen at the same temperature as that at which the oxidation was carried out to reduce the reducible elements of the composition to their lowest state of valency and produce a composite catalyst of" high activity and resistance to degeneration. Catalysts prepared in this manner are those which comprise a refrac- Complete descriptions ofA .tory, mixed oxides base composited to evince acidic prop- .erties and hydrocarbon cracking activity, having incorporatedtherein 2 to 10% of a hydrogenation component, such as group VIII metals of vthe iron period; oxides of Apolyvalent metals of Agroups V, VI and VII; and group VII-I metal(of the iron period) salts of oxyacids ofpoly- .valent metals of groupsV, VI, and VII. Specific ex- .amples of these hydrogenation components include cobalt, nickel; tungsten oxide, molybdenum oxide, chromium oxide, manganese oxide, vanadium oxide; and cobalt and Vnickel salts of the oxyacids of tun-gsten, molybdenum, gchromium, vanadium, and manganese, eg., nickel tung- .state, cobalt molybdate, nickel molybdate, etc. Suitable -refractory, acidic, mixed oxide'bases include but are not t SiOz-Aizoa, SiO2-ZI`O2, B203, A1203-'ZI'O2 A1203--BCO, A12O3B2O3, Cr03, B2O3-Ti02, SiO2Al203-Zr02, SiO2-Al2O3- .BeO, and acid-treated clays. These mixed oxides, in forming the base, can be either in chemical or physical combination. From a standpoint of activity, it has been ,found that catalyst carriers containing 50 to 87% silica and 50 Vto 13% alumina, having incorporated therein 3 to 5% of Ithe hydrogenation agent, are preferred. To facilitate the description of` these catalysts they will be referred vto as preconditioned, refractory, acidic, mixed oxides base-hydrogenation agent composite isomerization catalysts and so designated in the appended claims.

Operating conditions selected for the isomerization phase are those best suited for isomerization of normal pentane, hexane, and heptane. Accordingly, the following conditions are employed:

Range Preferred Temperature, F

Feed stocks which may be processed by the method of this invention include hydrocarbon mixtures contain- Ving saturated C5, C5, and C7 parainic hydrocarbons. Suitable feeds include petroleum-derived, hydrocarbon mixtures, such as natural gasolines, naphtha distillates boiling up to about 210 F., light catalytic reformate, f hydrogenated light coker naphtha, and others. Although it is preferable to stabilize the feed stock to remove the butane constituents, as is shown in the illustrated embodi- -ment where they are removed in the `deisopentizer, no .operational diculties arise if the butanes enter the reaction zone but they function as a diluent for the feed.

Also the presence of naphthenes, while not desirable be cause they load the reactor with a component that is not upgraded in octane number, causes no trouble.

The foregoing specific description of the instant invention involves the prefractionation of a suitable hydrocarbon feed stock to produce a low boiling fraction consisting essentially of n-pentane and `a consecutive, higheri boiling fraction containing n-hexane and n-heptane, and their subsequent respective isomerization under optimum catalytic conditions. It is to be understood, however, that other process variations can be utilized Without departing from the essence of this invention. For example, the higher-boiling fraction can be further fractionated into a separate fraction consisting essentially of n-hexane and a separate fraction consisting essentially of n-heptane. The reaction system for processing this plurality of x streams will still comprise the combination of catalysts described above except that a separate reactor containing preconditioned, refractory, acidic, mixed oxides basehydrogenation agent composite isomerization catalysts `Willybe employed for processing the n-hexane feed and n-heptane feed. A manipulative operation of this nature 10 boiling fraction.

will also require that the illustrated product recovery .system-be modiled to permit the recycle of the' n-paraf- 'finie constituents of the reaction etliuent to their respective reactors. l A I f Because the n-hexane yis receptive to being processed in the presencefoftheplatinum or palladium catalysts or vthe preconditioned, refractory, acidic, mixed oxides basehydrogenation agent composite isomerization catalysts, it may be desirable to include this constituentin the low- The adaptability of this component avoids the need for VpreciseY fractionators for exactly splitting the feed stock and permits the inclusion of this component in both'the low-boiling n-pentane-containing Vfraction and the high-boiling n-heptane-containing fraction.

By employing the processing scheme of this invention, advantage is taken of the effectiveness of platinumor palladium-containing catalysts for pentane isomerization at high space velocities. This permits relatively small amounts of catalysts to be required as compared with the amounts of preconditioned, refractory, acidic, mixed oxides base-hydrogenation agent composite isomerization catalysts required to attain the same severity of operation. On the other hand, these latter catalysts are especially effective for the isomerization of heptane, which is 'not as readily carried out in the presence of platinum or palladium catalysts. It VisV therefore apparent that the integrated, split-treatment isomerization process of this invention is more economical to construct and operate than are processes in which all components are subjected to the same isomerization conditions.

Accordingly, the process of this invention is claimed as: l. A method for enhancing the octane number characteristics of an isomerizable feed stock containingsubstantial amounts of C5, C5, and C7 saturated paratinic hydrocarbons which comprises fractionating said feed stock to produce a loW-boili-ng fraction containing npentane, 'and being substantially free from n-heptane, and a high-boiling fraction containing n-heptane and be- 40 ing substantially free from n-pentane, isomerizing said low-boiling fraction in the presence of a noble metal catalyst, consisting essentially of-arnetal selected from the group consisting of platinum land palladium on a suitable support, to produce a first reaction effluent, isomeriz- 4:5V ing said high-boiling inaction in the presence of a composite catalyst prepared by impregnating a refractory, acidic, mixed oxides base with a hydrogenation agent, and preconditioned by reduction, followed by oxidation at 650750 F., and vreduction-With hydrogen at 650- 750 F., to produce a second reaction eiuent, the isomerizing of said first and second fractions being carried out under the following conditions:

fnactionating the rst and second reaction effluents in a product recovery syst-em to recover a liquid product rich in branched-chain C5-C7 paraflinic hydrocarbons and having enhanced performance characteristics.

2. A method for enhancing the octane number characteristics of an isomerizable, hydrocarbon feed stock containing substantial Iamounts of normal C5, C5, and C7 saturated, parainic hydrocarbons which comprises fractionating said feed stock to produce a low-boiling fraction cons-isting essentially of n-pentane, and a high-boiling fraction containing n-hexane and n-heptane, isom- -erizing said low-boiling fraction inthe presence of a noble metal catalyst, consisting essentially of a metal selected carried out under the following conditions:

Low-Boiling High-Boiling Fraction Fraction Temperature, F 830-900 60G-750 Pressure, p.s.i.g.-..--- 20o-500 180-1, 000 Li nid Weight Hourly Space Velocity- 2- 0. 1-2.0 Hz hydrocarbon mole ratio 0. 1-0. 5 0. 1-4. 5

fractionating the first `and second reaction eiuents in a product recovery system to recover a liquid product rich in branched-chain Cs-Cq paranic hydrocarbons and having enhanced perfomance characteristics.

3. A method -for enhancing the octane number characteristics of an isomerizable, petroleum-derived feed stock containing substantial amounts of normal C5, C, and 'C1 saturated, parainic hydrocarbons which comprises fractionating said feed stock to produce a lowboiling fraction consisting essentially of n-pentane, and a high-boiling fraction containing yn-hexane and n-heptane, isomerizing said low-boiling fraction in the presence of a noble metal catalyst, consisting essentially of a metal selected from the group consisting of platinum and palladium on a suitable support, to produce a irst reaction etiiuent, isomerizing said high-boiling fraction in the presence of va composite catalyst prepared by impregnating a refractory, acidic, mixed oxides base with a hydrogeuation agent, and preconditioned by reduction, followed by oxidation at 650750 F., and reduction with hydrogen at 650-750 F., to produce a second reaction eiliuent, the isomerizing of said first and second fractions being carried out under the following conditions:

asesor.

V10 vtion agent, .and preconditioned by reduction, followed by oxidation'at 650-750 F., and reduction Iwith hydrogen at 650-750 F., to produce a second reaction eiuent, 'the somerizing of said iirstv and second fractions being carried out under the following conditions:

fractionating the iirst and second reaction eiuents in a product recovery system to recover a lliquid product rich in branched-chain C5-C7 paraiinic hydrocarbons and having enhanced performance characteristics.

6. A process in accordance with claim 5 in which said noble metal catalyst is platinum.

7. A process in accordance with claim 5 in which said preconditioned, composite isomerization catalyst is NiMoO., supported on silica-alumina.

8. A method for enhancing the octane number characteristics of an isomerizable petroleum-derived feed stock containing substantial amounts of normal C5, CG, and C7 saturated, paratiinic hydrocarbons which comprises fractionating said feed stock to produce a low-boiling iraction, consisting essentially of n-pentane and a high-boiling fraction containing n-hexane and n-heptane, isomerizing said llow-boiling fraction in the presence of a noble metal catalyst, consisting essentially of 0.1-1.0 Weight percent of platinum supported on an alumina carrier, to produce a tirst reaction eiiluent, isomerizing said high-boiling fraction in the presence of a composite catalyst prepared by impregnating a silica-alumina carrier with 2-l0% wt. of NiMoO4, and preconditoned by reduction, followed by oxidation at 650-750 F.,'

and reduction with hydrogen at 650-750 F., to produce -a second reaction effluent, the isomerizing of said first and second fractions being carried out under the following conditions:

Low-Boiling High-Boiling Low-Boiling High-Boiling Fraction Fraction Fraction Fraction Temperature, F 830-900 60o-750 Temperature, F S50-875 650-725 Pressure, p.s.i.g 20o-500 18o-1, ooo Pressure, p.s.i.g 35o-500 35o-750 Liquid Weight Hourly Space Velocity 2-10 0. 1-2.0 50 Liquid Weight Hourly Space Velocit 2-4 0. 5-1. 5 Iii/hydrocarbon mole ratio 0. 1-0. 5 0. 1-4. 5 Bfr/hydrocarbon mole ratio 0. 1-0. 5 0. 5-3. 5

' fractionating the first and second reaction eiiluents isn a product recovery system to recover a liquid product rich in branched-chain C-C, parainic hydrocarbons and having enhanced performance characteristics.

4. A process in `accordance with claim 3 in which said noble metal catalyst is platinum and said preconditioned, composite, isomeriziation catalyst is NiMoOq, supported on silica-alumina.

5. A method for 4enhancing the octane number characteristics of an isomerizable, petroleum-derived feed stock containing substantial amounts of normal C5, C6, and C7 saturated, parainic hydrocarbons which comprises fractionati-ng said feed stock to produce a lowboiling fraction consisting essentially of n-pentane, and a high-boiling fraction containing n-hexane and n-heptane, isomerizing said low-boiling fraction in the presence of a noble metal catalyst, consisting essentially of a metal selected from the group consisting of platinum and palladium on la suitable support, to produce a first reaction eluent, isomerizing said high-boiling fraction in the presence of a composite catalyst prepared by impregnating a refractory, acidic, mixed oxides base with a hydrogenateristics of an isomerizable feed stock containing about 20 vol. percent C5, 30 vol. percent C3, 30 vol. percent C, saturated parainic hydrocarbons and 20 vol. naphthenes, which comprises fractionating said feed stock to produce a :low boiling fraction containing n-pentane, and being substantially Ifree from n-heptane, and a high-boiling fraction containing n-heptane and being substantially free from n-pentane, isomerizing said low-boiling fraction in the presence of la noble metal catalyst, consisting essentially of 0.5% by weight of platinum supported on an alumina carrier to produce a first reaction eiliuent, isomerizing said high-boiling fraction in lthe presence of a composite catalyst prepared by impregnating a silicaalumina carrier with 10% Wt. of NiMoOg, and preconditioned by -reduction, followed by oxidation at 650-750 F., and reduction with hydrogen at 650-7 50 F., to produce a second reaction eiiuent, the isomenizing of said 4*fir-st and second fractions being carried out under the following conditions:

Low-Boiling fractionatfing the first and secondreacton eiuents in a .product recovery system to recover av `liquid productv rich in branched-chain Cs-Cfparanic hydrocarbons and having enhanced performance characteristics.

'y v References Cited in the le of this patent "UNITED STATES PATENTS Evenng runen, 1948 2,687,370 Hendricks V-- Aug. 24, 1954 1798;105 t 'Heinemann et a1. v V 1 July 21, 1957 'FOREIGN PATENTS v 4875392- YCanada Oct. 21, V1952 

1. A METHOD FOR ENHANCING THE OCTANE NUMBER CHARACTERISTICS OF AN ISOMERIZABLE FEED STOCK CONTAINING SUBSTANTIAL AMOUNTS OF C5, C6, AND C7 SATURATED PARAFFINIC HYDROCARBONS WHICH COMPRISES FRACTIONATING SAID FEED STOCK TO PRODUCE A LOW-BOILING FRACTION CONTAINING NPENTANE, AND BEING SUBSTANTIALLY FREE FROM N-HEPTANE, AND A HIGH-BOILING FRACTION CONTAINING N-HEPTANE AND BEING SUBSTANTIALLY FREE FROM N-PENTANE, ISOMERIZING SAID LOW-BOILING FRACTION IN THE PRESENCE OF A NOBLE METAL CATALYST, CONSISTING ESSENTIALLY OF A METAL SELECTED FROM THE GROUP CONSISTING OF PLATINUM AND PALLADIUM ON A SUITABLE SUPPORT, TO PRODUCE A FIRST REACTION EFFLUENT, ISOMERIZING SAID HIGH-BOILING FRACTION IN THE PRESENCE OF A COMPOSITE CATALYST PREPARED BY IMPREGNATING A REFRACTORY, ACIDIC, MIXED OXIDES BASE WITH A HYDROGENATION AGENT, AND PRECONDITIONED BY REDUCTION, FOLLOWED BY OXIDATION AT 650*-750*F., AND REDUCTION WITH HYDROGEN AT 650*- 